Planetary evolution with atmospheric photoevaporation

Context. Observations have revealed in the Kepler data a depleted region separating smaller super-Earths from larger sub-Neptunes. This can be explained as an evaporation valley between planets with and without H/He that is caused by atmospheric escape. Aims. We want to analytically derive the valley’s locus and understand how it depends on planetary properties and stellar X-ray and ultraviolet (XUV) luminosity. We also want to derive constraints for planet formation models. Methods. First, we conducted numerical simulations of the evolution of close-in low-mass planets with H/He undergoing escape. We performed parameter studies with grids in core mass and orbital separation, and we varied the postformation H/He mass, the strength of evaporation, and the atmospheric and core composition. Second, we developed an analytical model for the valley locus. Results. We find that the bottom of the valley quantified by the radius of the largest stripped core, Rbare, at a given orbital distance depends only weakly on postformation H/He mass. The reason is that a high initial H/He mass means that more gas needs to evaporate, but also that the planet density is lower, increasing mass loss. Regarding the stellar XUV-luminosity, Rbare is found to scale as LXUV0.135. The same weak dependency applies to the efficiency factor ε of energy-limited evaporation. As found numerically and analytically, Rbare varies a function of orbital period P for a constant ε as P−2pc∕3 ≈ P−0.18, where Mc ∝ Rcpc is the mass-radius relation of solid cores. We note that Rbare is about 1.7 R⊕ at a ten-day orbital period for an Earth-like composition. Conclusions. The numerical results are explained very well with the analytical model where complete evaporation occurs if the temporal integral over the stellar XUV irradiation that is absorbed by the planet is larger than the binding energy of the envelope in the gravitational potential of the core. The weak dependency on the postformation H/He means that the valley does not strongly constrain gas accretion during formation. But the weak dependency on primordial H/He mass, stellar LXUV, and ε could be the reason why the valley is so clearly visible observationally, and why various models find similar results theoretically. At the same time, given the large observed spread of LXUV, the dependency on it is still strong enough to explain why the valley is not completely empty.

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Search for intermittent X-ray pulsations from neutron stars in low-mass X-ray binaries

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.6 ◽

2021 ◽

Vol 38 ◽

Author(s):

Yunus Emre Bahar ◽

Manoneeta Chakraborty ◽

Ersin Göğüş

Keyword(s):

Neutron Stars ◽

Orbital Period ◽

Oscillation Frequency ◽

Orbital Motion ◽

X Rays ◽

X Ray ◽

Second Stage ◽

Corrected Data ◽

Low Mass ◽

X Ray Binaries

Abstract We present the results of our extensive binary orbital motion corrected pulsation search for 13 low-mass X-ray binaries. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1 122 Hz and have a binary orbital period varying from 2.1 to 18.9 h. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data.

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V479 And: CV, LMXB, or Symbiotic?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312014780 ◽

2011 ◽

Vol 7 (S281) ◽

pp. 113-116

Author(s):

Diego González Buitrago ◽

Gagik Tovmassian ◽

Juan Echevarría ◽

Sergey Zharikov ◽

Takamitsu Miyaji ◽

...

Keyword(s):

Orbital Period ◽

Main Sequence ◽

Compact Object ◽

Close Binary System ◽

Close Binary ◽

Stellar Winds ◽

Primary Star ◽

Giant Star ◽

X Ray ◽

Low Mass

AbstractV479 And is a 14.26 hour, close binary system, comprised of a G8-K0 star departing from the main sequence and a compact primary star accreting matter from the donor. The object is an X-ray source, modulated with the orbital period. This, and the presence of an intense He II line, leads us to speculate that the compact object is a magnetic white dwarf. However, we do not find strong constraints on the upper mass limit of the compact object, and we may have a neutron star in a low mass X-ray binary instead of a cataclysmic variable. The orbital period is certainly too short for the donor star to be an evolved giant star, so classifying this object as a symbiotic binary may be a big stretch; however there is an evidence that the mass transfer occurs via stellar winds, rather than through the L1 point of Roche filling secondary, a phenomenon more common for symbiotic stars.

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Modeling of Oxygen-Neon Dominated Accretion Disks in Ultracompact X-Ray Binaries: 4U 1626-67

International Astronomical Union Colloquium ◽

10.1017/s025292110015225x ◽

2004 ◽

Vol 194 ◽

pp. 146-147 ◽

Cited By ~ 2

Author(s):

K. Werner ◽

T. Nagel ◽

S. Dreizler ◽

T. Rauch

Keyword(s):

Accretion Disks ◽

Important Process ◽

Gravitational Settling ◽

X Ray ◽

The Core ◽

Synthetic Spectra ◽

First Results ◽

Low Mass ◽

X Ray Binaries

AbstractWe report on first results of computing synthetic spectra from H/He-poor accretion disks in ultracompact LMXBs. We aim at the determination of the chemical composition of the very low-mass donor star, which is the core of a former C/O white dwarf. The abundance analysis allows to draw conclusions on gravitational settling in WDs which is an important process affecting cooling times and pulsational g-mode periods.

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Optical Photometry of LMXBs: UW CrB (=MS 1603+260) and V1408 Aql (=4U 1957+115)

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2015.02.0050 ◽

2015 ◽

Vol 2 (1) ◽

pp. 50-54

Author(s):

P. A. Mason ◽

E. L. Robinson ◽

S. Gomez ◽

J. V. Segura

Keyword(s):

Black Hole ◽

Orbital Period ◽

Light Curves ◽

Optical Data ◽

Published Data ◽

Type I ◽

Optical Photometry ◽

Mean Intensity ◽

X Ray ◽

Low Mass

We present new optical observations of V1408 Aql (= 4U 1957+115), the only low mass X-ray binary, black hole candidate known to be in a persistently soft state. We combine new broadband optical photometry with previously published data and derive a precise orbital ephemeris. The optical light curves display sinusoidal variations modulated on the orbital period as well as large night to night changes in mean intensity. The amplitude of the variations increases with mean intensity while maintaining sinusoidal shape. Considering the set of constraints placed by the X-ray and optical data we argue that V1408 Aql may harbor a very low mass black hole. Optical light curves of UW CrB display partial eclipses of the accretion disk by the donor star that vary both in depth and orbital phase. The new eclipses of UW CrB in conjunction with published eclipse timings are well fitted with a linear ephemeris. We derive an upper limit to the rate of change of the orbital period. By including the newly observed type I bursts with published bursts in our analysis, we find that optical bursts are not observed between orbital phases 0.93 and 0.07, i.e. they are not observable during partial eclipses of the disk.

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A SCUBA survey of Orion – the low-mass end of the core mass function

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2006.11246.x ◽

2007 ◽

Vol 374 (4) ◽

pp. 1413-1420 ◽

Cited By ~ 162

Author(s):

D. Nutter ◽

D. Ward-Thompson

Keyword(s):

Mass Function ◽

Core Mass ◽

The Core ◽

Low Mass

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Formation of planetary populations – III. Core composition and atmospheric evaporation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2087 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4814-4833 ◽

Cited By ~ 2

Author(s):

Matthew Alessi ◽

Julie Inglis ◽

Ralph E Pudritz

Keyword(s):

Physical Factors ◽

Solid Core ◽

Core Composition ◽

Planetary Cores ◽

Short Period ◽

Wide Range ◽

Low Mass ◽

Orbital Periods ◽

Far Ultraviolet ◽

Gas Accretion

ABSTRACT The exoplanet mass–radius diagram reveals that super-Earths display a wide range of radii, and therefore mean densities, at a given mass. Using planet population synthesis models, we explore the key physical factors that shape this distribution: planets’ solid core compositions, and their atmospheric structure. For the former, we use equilibrium disc chemistry models to track accreted minerals on to planetary cores throughout the formation. For the latter, we track gas accretion during the formation and consider photoevaporation-driven atmospheric mass-loss to determine what portion of accreted gas escapes after the disc phase. We find that atmospheric stripping of Neptunes and sub-Saturns at small orbital radii (≲0.1 au) plays a key role in the formation of short-period super-Earths. Core compositions are strongly influenced by the trap in which they formed. We also find a separation between Earth-like planet compositions at small orbital radii ≲0.5 au and ice-rich planets (up to 50 per cent by mass) at larger orbits ∼1 au. This corresponds well with the Earth-like mean densities inferred from the observed position of the low-mass planet radius valley at small orbital periods. Our model produces planet radii comparable to observations at masses ∼1–3 M⊕. At larger masses, planets’ accreted gas significantly increases their radii to be larger than most of the observed data. While photoevaporation, affecting planets at small orbital radii ≲0.1 au, reduces a subset of these planets’ radii and improves our comparison, most planets in our computed populations are unaffected due to low-far ultraviolet fluxes as they form at larger separations.

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Heavy-metal Jupiters by major mergers: metallicity versus mass for giant planets

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2500 ◽

2020 ◽

Vol 498 (1) ◽

pp. 680-688 ◽

Cited By ~ 2

Author(s):

Sivan Ginzburg ◽

Eugene Chiang

Keyword(s):

Heavy Metal ◽

Accretion Rate ◽

Giant Planet ◽

Giant Planets ◽

Solid Core ◽

Core Mass ◽

The Core ◽

Multiple Cores ◽

Merger Rate ◽

Gas Accretion

ABSTRACT Some Jupiter-mass exoplanets contain ${\sim}100\, {\rm M}_{\hbox{$\oplus $}}$ of metals, well above the ${\sim}10\, {\rm M}_{\hbox{$\oplus $}}$ typically needed in a solid core to trigger giant planet formation by runaway gas accretion. We demonstrate that such ‘heavy-metal Jupiters’ can result from planetary mergers near ∼10 au. Multiple cores accreting gas at runaway rates gravitationally perturb one another on to crossing orbits such that the average merger rate equals the gas accretion rate. Concurrent mergers and gas accretion implies the core mass scales with the total planet mass as Mcore ∝ M1/5 – heavier planets harbour heavier cores, in agreement with the observed relation between total mass and metal mass. While the average gas giant merges about once to double its core, others may merge multiple times, as merger trees grow chaotically. We show that the dispersion of outcomes inherent in mergers can reproduce the large scatter in observed planet metallicities, assuming $3{-}30\, {\rm M}_{\hbox{$\oplus $}}$ pre-runaway cores. Mergers potentially correlate metallicity, eccentricity, and spin.

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Hydrogen Dominated Atmospheres on Terrestrial Mass Planets: Evidence, Origin and Evolution

Space Science Reviews ◽

10.1007/s11214-020-00756-w ◽

2020 ◽

Vol 216 (8) ◽

Cited By ~ 1

Author(s):

J. E. Owen ◽

I. F. Shaikhislamov ◽

H. Lammer ◽

L. Fossati ◽

M. L. Khodachenko

Keyword(s):

Solar System ◽

Large Population ◽

High Energy ◽

Terrestrial Planets ◽

Important Process ◽

X Ray ◽

Origin And Evolution ◽

Atmospheric Escape ◽

Low Mass ◽

High Energy Emission

AbstractThe discovery of thousands of highly irradiated, low-mass, exoplanets has led to the idea that atmospheric escape is an important process that can drive their evolution. Of particular interest is the inference from recent exoplanet detections that there is a large population of low mass planets possessing significant, hydrogen dominated atmospheres, even at masses as low as $\sim 2~\mbox{M}_{\oplus }$ ∼ 2 M ⊕ . The size of these hydrogen dominated atmospheres indicates the envelopes must have been accreted from the natal protoplanetary disc. This inference is in contradiction with the Solar System terrestrial planets, that did not reach their final masses before disc dispersal, and only accreted thin hydrogen dominated atmospheres. In this review, we discuss the evidence for hydrogen dominated atmospheres on terrestrial mass ($\lesssim 2~\mbox{M}_{\oplus }$ ≲ 2 M ⊕ ) planets. We then discuss the possible origins and evolution of these atmospheres with a focus on the role played by hydrodynamic atmospheric escape driven by the stellar high-energy emission (X-ray and EUV; XUV).

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Observations of Low Mass X-Ray Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100039117 ◽

1996 ◽

Vol 158 ◽

pp. 349-358

Author(s):

Alan P. Smale

Keyword(s):

Neutron Stars ◽

Orbital Period ◽

Binary Systems ◽

Light Curves ◽

X Ray ◽

Fast Timing ◽

Low Mass ◽

And Behavior ◽

X Ray Binaries

AbstractIn this paper I review the properties and behavior of low-mass X-ray binary systems (LMXBs) that contain neutron stars (NS), concentrating on the Galactic bulge sources and bursters. I describe the observed characteristics of LMXBs including their light curves, spectra, eclipses, dips, bursts, flares, pulsations, QPO, long-term periodicities and orbital period changes, and explain how fast timing results and the distinction between ‘Z’ and ‘atoll’-type sources provide the key to a unified model of LMXB behavior.

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